This invention relates to a processing solution having a bleaching ability for a light-sensitive silver halide color photographic material. More particularly, this invention pertains to an effective bleaching solution and bleach-fixing solution for a light-sensitive silver halide color photographic material which is improved in various processing performances and liquid characteristics.
In general, in order to obtain a color image by processing of a light-sensitive silver halide color photographic emulsion subjected to imagewise exposure, there is provided, after the step of color development, the step of processing the silver halide formed with a processing solution having a bleaching ability.
As the processing solution having a bleaching ability, a bleaching solution and a bleach-fixing solution are known. When a bleaching solution is used, the step of fixing of silver halide with a fixing agent is usually added subsequent to the bleaching step. On the other hand, with the use of a bleach-fixing solution, bleaching and fixing are effected in one step.
As the processing solution having a bleaching ability in processing of a light-sensitive silver halide color photographic material, there have widely been used inorganic oxidizing agents such as red prussiate, dichromate, persulfate, iron chloride, etc. which are oxidizing agents for bleaching the image silver.
However, it has been pointed out that the processing solution containing these inorganic oxidizing agents involve some serious drawbacks. For example, red prussiate and dichromate, although they are excellent in bleaching power of image silver, have the problem of being decomposed to form cyan ions or hexavalent chromium ions which may be harmful to human bodies, thus having unfavorable properties from the standpoint of prevention of pollution. Also, since these oxidizing agents have very strong oxidative power, it is difficult to permit a silver halide solubilizing agent such as a thiosulfate salt to coexist in the same processing solution. Therefore, it is almost impossible to use these oxidizing agents in a bleach-fixing bath, whereby the objects of speed-up and simplification of processing can hardly be accomplished. Further, the processing solution containing these inorganic oxidizing agents has also another drawback that it is difficult to reuse the waste liquor after processing without being discarded.
In contrast, a processing solution is coming into use which causes little problem in pollution and also meets the requirements of rapid and simple processing as well as enabling regeneration and reuse, which contains a metal complex salt of an organic acid such as an aminopolycarboxylic acid metal complex salt, etc. However, a processing solution utilizing a metal complex salt of an organic acid has a moderate oxidizing power and therefore has the drawback of slow bleaching speed (oxidizing speed) of the image silver (metal silver) formed in the developing step. For example, ethylenediaminetetraacetic acid iron (III) complex salt, which is considered to have a potent bleaching power among the aminopolycarboxylic acid metal complexe salts, is utilized as the bleaching solution and bleach-fixing solution in some practical applications. However, it is deficient in bleaching action in high sensitivity light-sensitive silver halide color photographic materials composed primarily of silver bromide or silver iodobromide emulsions, particularly color paper for photographing, color negative film for photographing and color reversal film containing silver iodide, whereby traces of image silver will remain even after prolonged processing to give poor silver elimination characteristic. This tendency will appear particularly markedly because of lowering in redox potential in a bleach-fixing solution where an oxidizing agent and a thiosulfate or thiosulfite coexist.
On the other hand, enormous effors have been made in developing a bleaching promoter for increasing the silver bleaching power of a bleaching solution or a bleach-fixing solution containing a metal complex salt of an organic acid, but no satisfactory result has yet been obtained.
Among the aminopolycarboxylic acids metal salt complexes, the present inventors have found diethylenetriaminepentaacetic acid iron (III) complex salt as an oxidizing agent having excellent oxidizing power particularly at higher pH region. A bleaching solution and a bleach-fixing solution containing diethylenetriaminepentaacetic acid iron (III) complex salt as the oxidizing agent has very excellent performances such as rapid silver bleaching reaction, little generation of stain when subjected directly to bleaching processing and further good storage stability of the bleach-fixing solution. However, when diethylenetriaminepentaacetic acid iron (III) complex salt is used as the oxidizing agent in a bleaching solution or a bleach-fixing solution, it was found that yellow staining, probably caused by coloration of iron (III) complex salt, was liable to occur. In particular, in the case of shortage of washing water, marked yellow staining is observed as a serious problem in photographic performance. Accordingly, it would be very desirable to develop a technique which can prevent yellow staining by diethylenetriaminepentaacetic acid iron (III) complex salt, and does not impair the silver bleaching ability, stain resistance and liquid storability of diethylenetriaminepentaacetic acid iron (III) complex salt.
Further, a bleaching solution and a bleach-fixing solution containing a diethylenetriaminepentaacetic acid iron (III) complex salt as the oxidizing agent has excellent performances that it is rapid in silver bleaching reaction at pH 4 or higher, particularly at pH 7 or higher, little in generation of stain when subjected directly to bleaching treatment and further good in storage stability of the bleach-fixing solution. However, it has now been revealed that when such a bleaching solution or a bleach-fixing solution is used and continuous processing is performed by an automatic developing machine, lowering in silver bleaching power and the so-called bad color restoration occur, which is a phenomenon such that the cyan dye converted to leuco form cannot sufficiently color formed by bleaching or bleach-fixing processing. The lowering in bleaching power and bad color restoration will occur particularly markedly when continuous processing is continued over a long time.
The present inventors have made studies over the causes for generation of such troubles. It has now been found that the diethylenetriaminepentaacetic acid iron (II) complex salt formed by silver bleaching reaction cannot be sufficiently oxidized into the diethylenetriaminepentaacetic iron (III) complex salt, whereby the diethylenetriaminepentaacetic acid iron (II) complex salt will be accumulated in the emulsion, or the bleaching solution or the bleach-fixing solution to cause the troubles as mentioned above. Therefore, in order to practically utilize a diethylenetriaminepentaacetic acid iron (III) complex salt for a bleaching solution or a bleach-fixing solution, it would also be very desirable to have a technique to promote markedly the air oxidation rate of a diethylenetriaminepentaacetic acid iron (II) complex salt.